In designing a circuit, it is often desired that some of N-P-N transistors included in a bipolar type IC can be used as N-P-N transistors of high current gain (h.sub.FE). In case of manufacturing an IC including such N-P-N transistor higher in h.sub.FE than the main constituent N-P-N transistors, it has heretofore been a particle that, while the manufacture of the main constituent N-P-N transistors is carried out, a P-type diffused layer for the base (or an N-type diffused layer for the emitter) of the high h.sub.FE N-P-N transistor is formed by a mask diffusion step separate from that for P-type diffused layers for the bases (or N-type diffused layers for the emitters) of the main constituent N-P-N transistors of the main constitutent N-P-N transistors, in order to make the base width of the high h.sub.FE N-P-N transistor small.
Due to the increased mask diffusion steps, however, the method of manufacturing the IC involves such disadvantages that the manufacturing process becomes complicated and that the characteristics of other elements within the IC are degraded.